Q-switched solid-state lasers are well known and have been demonstrated successfully for many laser micromachining applications. However, micromachining parameters for Q-switched lasers, including their wavelengths (ranging from near infrared to deep ultraviolet), pulsewidths, pulse energies, and pulse repetition rates, have still not been perfected for certain classes of layered organic, inorganic, and metallic microelectronic material constructions with respect to throughput and machining quality, such as cleanness, sidewall taper, roundness, and repeatability.
One such class of materials, commonly used in the printed wiring board (PWB) industry, includes glass cloth impregnated with one or more organic polymer resins that is sandwiched between conductive metal layers, typically copper. This material configuration is known as “FR4” or “BT.”
Another class, commonly used as packaging materials for high-performance integrated circuits, includes unfired, “green” ceramic materials. These ceramic substrates are formed by high-pressure pressing of powders of common ceramics such as aluminum oxide (Al2O3) or aluminum nitride (AlN). The micron- or submicron-scale particles are held together with organic “binders” that provide sufficient mechanical integrity for machining operations such as via drilling. Afterward, the green material is fired at high temperature, driving off the binders and fusing or sintering the microparticles together into an extremely strong, durable, high-temperature substrate.
U.S. Pat. Nos. 5,593,606 and 5,841,099 of Owen et al. describe techniques and advantages for employing Q-switched UV laser systems to generate laser output pulses within advantageous parameters to form through-hole or blind vias through at least two types of layers in multilayer devices, including FR4. These patents discuss these devices and the lasers and parameters for machining them. These parameters generally include nonexcimer output pulses having temporal pulsewidths of shorter than 100 nanoseconds (ns), spot areas with spot diameters of less than 100 microns (μm), and average intensities or irradiances of greater than 100 milliwatts (mW) over the spot areas at repetition rates of greater than 200 hertz (Hz).
U.S. Pat. No. 6,784,399 of Dunsky et al. discloses the use of a Q-switched carbon dioxide laser to produce bursts of laser pulses whose spikes and tails can be controlled to address disparate vaporization temperatures or melting points of the bulk via material.
U.S. Pat. No. 5,656,186 of Mourou et al. discloses a general method of laser-induced breakdown and ablation at several wavelengths by high-repetition-rate ultrafast laser pulses, typically shorter than 10 picoseconds (ps), and demonstrates creation of machined feature sizes that are smaller than the diffraction limited spot size.
U.S. Pat. No. 5,742,634 of Rieger et al. discloses a simultaneously Q-switched and mode-locked neodymium laser device with diode pumping. The laser emits a series of pulses, each having a duration time of 60 to 300 ps, under a time duration of 100 ns.
U.S. Pat. No. 6,574,250 of Sun et al. is the first to disclose a method for processing links on-the-fly with at least two laser pulses. One embodiment employs pulses having pulsewidths shorter than 25 picoseconds (ps).
U.S. Pat. No. 6,734,387 of Kafka et al. discloses the use of UV picosecond laser output from a mode-locked, quasi-continuous wave (cw) laser system to cut or scribe lines in polymeric films.